Giant magnetoresistive sensor, thin-film read/write head and magnetic recording apparatus using the sensor

ABSTRACT

A giant magnetoresistive sensor which is improved in reproduction output and peak asymmetry of read-back waveform. It is composed of a first free ferromagnetic film, a first non-magnetic film, a composite ferromagnetic film, a second non-magnetic film, and a second free ferromagnetic film, which are laminated sequentially, but has no antiferromagnetic film to fix said composite ferromagnetic film, and said composite ferromagnetic film contains a first, second, and third ferromagnetic film, which are antiferromagnetically coupled with one another, and also contains films which separate said ferromagnetic films from one another and antiferromagnetically couple them with one another.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a magnetic head to record andreproduce information on and from a magnetic recording medium, and moreparticularly to an improved giant magnetoresistive sensor and a magneticrecording/reproducing apparatus equipped with said sensor.

[0003] 2. Description of the Related Art

[0004] The increasing magnetic recording density requires a highlysensitive magnetic head for reproduction. The one meeting thisrequirement is described in “Giant magnetoresistance in soft magneticmulti-layer film”, Physical Review B, vol. 43, pp. 1297-1300. It isconstructed such that two magnetic layers are separated by onenonmagnetic layer and an exchange bias magnetic field is applied to oneof the magnetic layers from an antiferromagnetic layer. This type ofmulti-layer film has resistance R with a component varying in proportionto cos θ, with θ being an angle between the directions of magnetizationof the two magnetic layers, according to the aforesaid thesis. Thisphenomenon is referred to as giant magnetoresistance (GMR).

[0005] A conventional giant magnetoresistive sensor is shown in FIG. 7.It consists of a substrate 5 and several layers sequentially formedthereon. Adjacent to the substrate are a magnetic shield layer 10 and amagnetic gap layer 20. On the magnetic gap layer 20 is amagnetoresistive film 30, which consists of a ferromagnetic film (freelayer) 35, a copper layer 40, a ferromagnetic film (pinned layer) 65,and an antiferromagnetic film 70, which are formed sequentially one overanother. The arrow 55 indicates the direction of magnetization. With themagnetoresistive film 30 patterned, there are arranged an electrode film90 and a permanent magnet layer 80 at each side thereof. The top iscovered with a magnetic gap layer 100 and a magnetic shield layer 110.The magnetoresistive film mentioned above is characterized in that thepinned layer has its magnetization pinned in the direction of elementheight (depth) by the exchange bias magnetic field from theantiferromagnetic layer. In general, the free layer has the axis of easymagnetization parallel to the cross-track direction (z direction) of thehead.

[0006] In the case of the head mentioned above, it is desirable that themagnetization in the entire free layer be kept parallel to thecross-track direction of the head so that the free layer does not suffermagnetic saturation when a signal magnetic field from the medium isapplied upward and downward in the direction of the element height ofthe head. Unfortunately, the magnetization in the free layer does notbecome uniformly parallel to the cross-track direction of the headbecause the free layer receives a static magnetic field which occurs asthe pinned layer (orienting vertically to the medium surface) becomesmagnetized. The result is that the head becomes sensitive unequally tothe positive and negative magnetic fields and reproduces a large peakasymmetry of read-back waveform. This not only adversely affects theimprovement of error rate by signal processing such as PRML (partialresponse sampling plus maximum likelihood detection) but also lowers theoutput. The peak asymmetry of read-back waveform is defined as follows.

[0007]Asym.=|V ⁺ −V ⁻ |/|V ⁺+V⁻|

[0008] (where V⁺ denotes the peak value of the positive output and V⁻denotes the peak value of the negative output.)

[0009] There is disclosed in Japanese Patent Laid-open No. 169026/1995 agiant magnetoresistive sensor designed to reduce the peak asymmetry ofread-back waveform. As shown in FIG. 8, it has a magnetoresistive film30 consisting of a ferromagnetic film (free layer) 35, a copper layer40, a composite ferromagnetic film (pinned layer) 50, and anantiferromagnetic film 70. The pinned layer 50, which is a compositeferromagnetic film, consists of two ferromagnetic films 51 and 53 (of Coor the like) and a non-magnetic layer 52 (or Ru or the like), the formerhaving their magnetization strongly coupled in the antiparalleldirection through the latter. The two ferromagnetic films producemagnetic moments aligning in the antiparallel direction, therebycanceling out each other. The result is a reduction of static magneticfield applied to the free layer from the pinned layer. The secondferromagnetic film 53 of the pinned layer 50 has its magnetizationpinned by the antiferromagnetic film 70.

[0010] There is disclosed in Japanese Patent Laid-open No. 7235/1996another giant magnetoresistive sensor designed to reduce the peakasymmetry of read-back waveform. As shown in FIG. 9, it has amagnetoresistive film 30 consisting of a ferromagnetic film (free layer)35, a copper layer 40, and a composite ferromagnetic film (pinned layer)50. The pinned layer 50, which is a composite ferromagnetic film,consists of two ferromagnetic films 51 and 53 (of Co or the like) and anon-magnetic layer 52 (or Ru or the like), the former having theirmagnetization strongly coupled in the antiparallel direction through thelatter, like the aforesaid head. The two ferromagnetic films 51 and 53should have an adequate thickness, so that the pinned layer has a largeeffective coercive force for it to be of self-pinned type. The result isa reduction of static magnetic field applied from the pinned layer andobviation of the antiferromagnetic film to fix the pinned layer. Theadvantage is a reduction of the entire film thickness of the head and areduction of the gap length.

[0011] On the other hand, there is disclosed in Japanese PatentLaid-open No. 347013/1993 and U.S. Pat. No. 5,287,238 a giantmagnetoresistive sensor designed to increase its reproducing output. Asshown in FIG. 10, it has a magnetoresistive film 30 consisting of afirst antiferromagnetic layer 70, a first pinned ferromagnetic film 65,a non-magnetic film 40, a free ferromagnetic film 35, a non-magneticlayer 40, a second pinned ferromagnetic film 66, and a secondantiferromagnetic film 71. The multi-layer structure, with the freelayer being held between the pinned layers, causes electrons to scatterover a larger area of interface. This tends to a larger relative changeof magnetoresistance (ΔR/R in percent) and a larger output ofreproduction. This type of giant magnetoresistive sensor is called dualspin valve (SV) head.

[0012] Another type of dual spin valve (SV) head is disclosed inJapanese Patent Laid-open No. 225925/1995. As shown in FIG. 11, it has amagnetoresistive film 30 consisting of a first free magnetic film 35, anon-magnetic film 40, a first ferromagnetic pinned film 65, anantiferromagnetic film 70, a second ferromagnetic pinned layer 66, anon-magnetic film 40, and a second free magnetic film 36. As in theforegoing head, the multi-layer structure, with the antiferromagneticfilm being held between the pinned layers and the free layers, causeselectrons to scatter over a larger area of interface. This tends to alarger relative change of magnetoresistance (ΔR/R in percent).

SUMMARY OF THE INVENTION

[0013] The disadvantage of the aforesaid structure, with the free layeror antiferromagnetic film being held between two upper and lower pinnedlayers, is that the static magnetic field applied to the thickness ofthe free layer from the pinned layer increases as the pinned layerincreases. Consequently, the direction of magnetization of the freelayer deviates from the direction of the track width of the head, withthe result that the peak asymmetry of reproduced signals becomes larger.The larger the asymmetry, the lower the read-back output.

[0014] A dual spin valve film to remedy the peak asymmetry of read-backwaveform is described in “PtMn dual spin valve film with a Co/Ru/Colaminated ferri pinned magnetic layer”, Synopsis of the 22^(nd) LectureMeeting of Japan Institute of Applied Magnetism, p. 309. As shown inFIG. 12, it has a magnetoresistive film 30 consisting of a firstantiferromagnetic film 70, a first composite ferromagnetic film (pinnedlayer) 50, a non-magnetic film 40, a ferromagnetic film (free layer) 35,a non-magnetic film 40, a second composite ferromagnetic film (pinnedlayer) 60, and a second antiferromagnetic film 71. The compositeferromagnetic films 50 and 60 have the same structure as the aforesaidcomposite film shown in FIG. 8. This structure is intended to reduce thestatic magnetic field from the pinned layer, thereby remedying the peakasymmetry of the read-back waveform of the head.

[0015] The disadvantage of the composite film functioning as the upperand lower pinned layers in the dual spin valve head is that the overallfilm thickness of the magnetic head increases. Any attempt to compensatethe increased thickness by reduction in the thickness of the magneticgap layers 20 and 100 shown in FIG. 7 ends up with an insufficientelectro-static durability which leads to electro-static destruction dueto short-circuits between the magnetoresistive film and shield film.

[0016] It is an object of the present invention to provide a giantmagnetoresistive sensor of dual spin valve type which excels inelectro-static durability and peak symmetry of read-back waveform.

[0017] The giant magnetoresistive sensor has a magnetoresistive filmconsisting of a substrate, a first free ferromagnetic film, a firstnon-magnetic film, a composite ferromagnetic film, a second non-magneticfilm, and a second free ferromagnetic film, which are formedsequentially one over another, so that the composite ferromagnetic filmbecomes the pinned layer of self-pinned type. The pinned layer ofself-pinned type consists of a first, second, and third ferromagneticfilms antiferromagnetically coupled with one another and filmsseparating these three ferromagnetic films and antiferromagneticallycoupling them with one another.

[0018] According to the present invention, the giant magnetoresistivesensor may also have a magnetoresistive film consisting of a substrate,a first composite ferromagnetic film, a first non-magnetic film, a freeferromagnetic film, a second non-magnetic film, and a second compositeferromagnetic film, which are laminated one over another. The aforesaidfirst and second composite ferromagnetic films should be the pinnedlayer of self-pinned type. The pinned layer of self-pinned type consistsof a first and second ferromagnetic films antiferromagnetically coupledwith each other and a film separating these two ferromagnetic films andantiferromagnetically coupling them with each other. Either of the firstand second composite ferromagnetic films may be replaced by theconventional pinned layer in which a singe pinned ferromagnetic film ispinned by an antiferromagnetic film.

[0019] The giant magnetoresistive sensor of the present invention ischaracterized in that the net amount of magnetic moment of the aforesaidcomposite ferromagnetic film can be made smaller than the total amountof magnetic moment of each ferromagnetic film in the compositeferromagnetic film. The composite film is regarded as one magneticentity responsible for the net magnetic moment.

[0020] Also, the giant magnetoresistive sensor of the present inventionmay be constructed such that the first and second ferromagnetic films ofthe aforesaid magnetic composite layer have almost the same magneticmoment and consequently the net magnetic moment of the aforesaidcomposite ferromagnetic film is nearly null.

[0021] The giant magnetoresistive sensor of the present invention shouldhave the aforesaid antiferromagnetic film such that it produces greatunidirectional anisotropy regardless of the order of lamination of theantiferromagnetic film and the ferromagnetic film. It should preferablybe made of nickel oxide, PtMn, PtPdMn, CrMnPt, or the like.

[0022] In addition, the giant magnetoresistive sensor of the presentinvention may be combined with a thin-film head of induction type formagnetic recording so as to constitute a thin-film magnetic head.

[0023] The giant magnetoresistive sensor of dual spin valve head typemay have a composite film of self-pinned type as the pinned layer. Theresult is a reduction of static magnetic field from the pinned layer andhence a remedy for peak asymmetry of read-back waveform. Another resultis a reduction of the total film thickness of the magnetoresistive film.This permits the insulating film between the magnetoresistive film andshield film to be thicker, and the thicker insulating film contributesto electro-static durability.

[0024] While the conventional dual spin valve head shown in FIG. 11 hasthe disadvantage that the scattering of electrons not contributing tothe relative change of magnetoresistance takes place in theantiferromagnetic film 70, the giant magnetoresistive sensor of thepresent invention shown in FIG. 1 is free from this disadvantage owingto the two free layers formed on both sides of the self-pinned layer andhence it has a better relative change of magnetoresistance than theconventional one.

[0025] In addition, according to the present invention, it is possibleto control the peak symmetry of read-back waveform if the staticmagnetic field applied to the free layer from the pinned layer isregulated by changing the difference in thickness of the two or threeferromagnetic films in the composite film of the pinned layer ofself-pinned type.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a sectional view of the giant magnetoresistive sensor inone embodiment of the present invention.

[0027]FIG. 2 is a sectional view of the giant magnetoresistive sensor inanother embodiment of the present invention.

[0028]FIG. 3 is a sectional view of the giant magnetoresistive sensor inanother embodiment of the present invention.

[0029]FIG. 4 is a sectional view of the giant magnetoresistive sensor inanother embodiment of the present invention.

[0030]FIG. 5 is a perspective view showing the structure of thethin-film magnetic head equipped with the giant magnetoresistive sensorof the present invention.

[0031]FIG. 6 is a schematic drawing of the read/write apparatus.

[0032]FIG. 7 is a sectional view of a conventional giantmagnetoresistive sensor.

[0033]FIG. 8 is a sectional view showing a magnetoresistive film in aconventional giant magnetoresistive sensor with a pinned layer ofcomposite film.

[0034]FIG. 9 is a sectional view showing a magnetoresistive film in aconventional giant magnetoresistive sensor with a pinned layer ofcomposite film.

[0035]FIG. 10 is a sectional view showing a magnetoresistive film in aconventional giant magnetoresistive sensor of dual spin valve type.

[0036]FIG. 11 is a sectional view showing a magnetoresistive film in aconventional giant magnetoresistive sensor of dual spin valve type.

[0037]FIG. 12 is a sectional view showing a magnetoresistive film in aconventional giant magnetoresistive sensor of dual spin valve type.

[0038]FIG. 13 is a graph showing the dependence of the normalized outputand peak asymmetry of read-out waveform on the sensor height hMR in thegiant magnetoresistive sensor in the example of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0039] The invention will be described in more detail with reference tothe following examples.

EXAMPLE 1

[0040] A typical giant magnetoresistive sensor of the present inventionis shown in section in FIG. 1. There is shown a substrate 5. On thesubstrate 5 are formed sequentially a lower shield film (NiFe film) 10,an insulating film (Al₂O₃ film) 20 for magnetic gap, and amagnetoresistive film 30. The magnetoresistive film 30 is composed of afirst free ferromagnetic film (NiFeCo) 35, a copper layer 40, acomposite ferromagnetic film (pinned layer of self-pinned type) 50, acopper layer 40, and a second free ferromagnetic film (NiFeCo) 45, whichare sequentially formed one over another. The composite ferromagneticfilm (pinned layer of self-pinned type) 50 is composed of Co 51 (25 Å),Ru 52 (6 Å), Co 53 (30 Å), Ru 52 (6 Å), and Co 54 (25 Å), which arelaminated sequentially. During lamination a magnetic field is applied inthe direction of the arrow 200. Owing to the applied magnetic field, thecomposite ferromagnetic film has its axis of easy magnetization orientedin the direction perpendicular to the paper surface. An organic resistfilm is laminated, and then it is patterned as desired. A film ofpermanent magnet (CoCrPt film) 80 is laminated. It is fabricated in adesired shape. A layer of Nb/Au/Nb is laminated, and then it isfabricated to form an electrode 90. An insulating film (Al₂O₃ film) 100for magnetic gap is formed. An upper shield film (NiFe film) 110 islaminated and then it is fabricated in a desired shape. Thus there isobtained a magnetic head. The electrode spacing Tw is 0.5 μm and thesensor height hMR is 0.4 μm.

[0041] The arrows 55 in the figure denote the direction of magnetizationof each magnetic film. In the composite ferromagnetic film 50, thefirst, second, and third ferromagnetic films are strongly coupled withone another in an antiferromagnetic manner, and hence magnetizationtakes place in the direction shown. The composite ferromagnetic film 50has a large effective coercive force and forms the pinned layer ofself-pinned type.

[0042] The head of the present invention was compared with a giantmagnetoresistive sensor of conventional type which has the sameelectrode spacing and sensor height (shown in FIG. 7). It was found thatthe head of the present invention produces 1.5 times as large read-backoutput as the conventional one.

[0043] A large number of heads varying in hMR were prepared, and theywere tested for peak-asymmetry of read-back waveform (Asym.) andread-back output. The results are shown in FIG. 13. Asym. is defined asfollows:

Asym.=|V ⁺ −V ⁻ |/|V ⁺ +V ⁻|

[0044] (where V⁺ denotes the peak value of the positive output and V⁻denotes the peak value of the negative output.) The read-back output isthe value normalized such that the value of the conventional head (withhMR being 0.4 μm) is 1. In the case of the conventional head, it isdifficult to make Asym. null. In addition, Asym. greatly changes as hMRchanges. By contrast, the head of the present invention keeps Asym.almost null. Even when hMR changes from 0.2 μm to 0.7 μm, Asym. changesvery little. This makes it possible to reduce the fluctuation of Asym.due to tolerance of hMR. The read-back output is about 1.5 times largerthan that in the conventional case. As mentioned above, this examplegives a giant magnetoresistive sensor with small peak asymmetry andlarge read-back output. In addition, this example gives a giantmagnetoresistive sensor superior in electro-static durability.

EXAMPLE 2

[0045] This example demonstrates another giant magnetoresistive sensorwhich differs in the thickness of the pinned layer from the one inExample 1. As in Example 1 shown in FIG. 1, it consists of a substrate5, a lower shield film (NiFe film) 10, an insulating film (Al₂O₃) 20 formagnetic gap, and a magnetoresistive film 30. The magnetoresistive film30 consists of a first free ferromagnetic layer (NiFeCo) 35, a copperlayer 40, a composite ferromagnetic film (pinned layer of self-pinnedtype) 50, and a copper layer 40, and a second free ferromagnetic filmNiFeCo) 55, which are laminated sequentially. The compositeferromagnetic film (pinned layer of self-pinned type) 50 consists of Co51 (20 Å), Ru 52 (6 Å), Co 53 (35 ÅA), Ru 52 (6 Å), and Co 54 (20 Å),which are laminated sequentially. During lamination a magnetic field isapplied in the direction of the arrow 200. Owing to the applied magneticfield, the composite ferromagnetic film has its axis of easymagnetization oriented in the direction perpendicular to the papersurface. An organic resist film is laminated, and then it is patternedas desired. A film of permanent magnet (CoCrPt film) 80 is laminated. Itis fabricated in a desired shape. A layer of Nb/Au/Nb is laminated, andthen it is fabricated to form an electrode 90. An insulating film (Al₂O₃film) 100 for magnetic gap is formed. An upper shield film (NiFe film)110 is laminated and then it is fabricated in a desired shape. Thusthere is obtained a magnetic head. The electrode spacing Tw is 0.5 μmand the sensor height hMR is 0.4 μm.

[0046] It was found that in this example, too, the compositeferromagnetic film 50 has a large effective coercive force and forms thepinned layer of self-pinned type for stable operation. It was also foundthat the giant magnetoresistive sensor produces 1.5 times as largeread-back output as the conventional one and has good electro-staticdurability and good Asym.

EXAMPLE 3

[0047] This example demonstrates another giant magnetoresistive sensorwhose sectional view is shown in FIG. 2. It consists of a substrate 5, alower shield film (NiFe film) 10, an insulating film (Al₂O₃) 20 formagnetic gap, and a magnetoresistive film 30. The magnetoresistive film30 consists of a first composite ferromagnetic film (pinned layer) 50, acopper layer 40, a free ferromagnetic film (NiFeCo) 35, a copper layer40, and a second composite ferromagnetic film (pinned layer) 60, whichare laminated sequentially. The first composite ferromagnetic film(pinned layer) 50 consists of Co 51 (20 Å), Ru 52 (6 Å), and Co 53 (35Å), which are laminated sequentially. During lamination a magnetic fieldis applied in the direction of the arrow 200. Owing to the appliedmagnetic field, the composite ferromagnetic film 50 has its axis of easymagnetization oriented in the direction perpendicular to the papersurface. The Co film 51 and the Co film 53 are strongly coupled witheach other in an antiferromagnetic manner, and hence magnetization takesplace in the direction shown. The composite ferromagnetic film 50 has alarge effective coercive force and forms the pinned layer of self-pinnedtype. Likewise, the second composite ferromagnetic film (pinned layer)60 consists of Co 61 (20 Å), Ru 62 (6 Å), and Co 63 (35 Å), which arelaminated sequentially. During lamination a magnetic field is applied inthe direction of the arrow 201. Owing to the applied magnetic field, thecomposite ferromagnetic film 60 has its axis of easy magnetizationoriented in the direction perpendicular to the paper surface, andmagnetization takes place in the direction shown. As in the case of thecomposite ferromagnetic film 50, the composite ferromagnetic film 60forms the pinned layer of self-pinned type. The first and secondferromagnetic composite films produce effective magnetic moments intheir antiparallel direction. This cancels out the magnetic fieldapplied to the free layer from the composite ferromagnetic film.

[0048] Subsequently, an organic resist film is laminated, and then it ispatterned as desired. A film of permanent magnet (CoCrPt film) 80 islaminated. It is fabricated in a desired shape. A layer of Nb/Au/Nb islaminated, and then it is fabricated to form an electrode 90. Aninsulating film (Al₂O₃ film) 100 for magnetic gap is formed. An uppershield film (NiFe film) 110 is laminated and then it is fabricated in adesired shape. Thus there is obtained a magnetic head. The electrodespacing Tw is 0.5 μm and the sensor height hMR is 0.4 μm.

[0049] It was found that in this example, too, the giantmagnetoresistive sensor produces 1.5 times as large read-back output asthe conventional one and has good electro-static durability and goodAsym.

[0050] Further, this example also demonstrates another giantmagnetoresistive sensor which is identical in structure with theabove-mentioned one, except that the thickness of the Co film in thefirst and second composite ferromagnetic film varies so that theeffective magnetic moment of the composite ferromagnetic film varies. Inthe first case, the first and second composite ferromagnetic filmsproduce the effective magnetic moment in the same direction. In thesecond case, the first and second magnetic composite layers have the twoCo films of the same thickness so that their effective magnetic momentis nearly null. In the third case, either of the composite ferromagneticfilms has an effective magnetic moment which is almost null. In all thecases, the resulting giant magnetoresistive sensor produces a largeread-back output and has good electro-static durability and good Asym.

EXAMPLE 4

[0051] This example demonstrates another giant magnetoresistive sensorwhose sectional view is shown in FIG. 3. It consists of a substrate 5, alower shield film (NiFe film) 10, an insulating film (Al₂O₃) 20 formagnetic gap, and a magnetoresistive film 30. The magnetoresistive film30 consists of a composite ferromagnetic film (pinned layer) 50, acopper layer 40, a free ferromagnetic film NiFeCo) 35, a copper layer40, a pinned ferromagnetic film (CoFe) 65, and an antiferromagnetic film(CrMnPt) 70, which are laminated sequentially. The compositeferromagnetic film (pinned layer) 50 consists of Co 51 (20 Å), Ru 52 (6Å), and Co 53 (35 Å), which are laminated sequentially. Duringlamination a magnetic field is applied in the direction of the arrow200. Owing to the applied magnetic field, the composite ferromagneticfilm 50 has its axis of easy magnetization oriented in the directionperpendicular to the paper surface. The Co film 51 and the Co film 53are strongly coupled with each other in an antiferromagnetic manner, sothat they form a pinned layer of self-pinned type. Subsequently, anorganic resist film is laminated, and then it is patterned as desired. Afilm of permanent magnet (CoCrPt film) 80 is laminated. It is fabricatedin a desired shape. A layer of Nb/Au/Nb is laminated, and then it isfabricated to form an electrode 90. An insulating film (Al₂O₃ film) 100for magnetic gap is formed. An upper shield film (NiFe film) 110 islaminated and then it is fabricated in a desired shape. Thus there isobtained a magnetic head. The electrode spacing Tw is 0.5 μm and thesensor height hMR is 0.4 μm.

[0052] In this example, the pinned ferromagnetic layer 65 is magnetizedin the direction of the arrow 55. However, this direction may bereversed (180°).

[0053] It was found that the giant magnetoresistive sensor in thisexample produces 1.5 times as large read-back output as the conventionalone and has good electro-static durability and good Asym.

[0054] Further, this example also demonstrates another giantmagnetoresistive sensor which is identical in structure with theabove-mentioned one, except that the thickness of the ferromagnetic filmis changed (Co 20 Å, Ru 6 Å, Co 25 Å) so that the effective magneticmoment of the composite ferromagnetic film 50 is almost null. The giantmagnetoresistive sensor produces a large read-back output and has goodelectro-static durability and good Asym.

EXAMPLE 5

[0055] This example demonstrates another giant magnetoresistive sensorwhose sectional view is shown in FIG. 4. It consists of a substrate 5, alower shield film (NiFe film) 10, an insulating film (Al₂O₃) 20 formagnetic gap, and a magnetoresistive film 30. The magnetoresistive film30 consists of an antiferromagnetic layer (CrMnPt) 70, a pinnedferromagnetic layer (CoFe) 65, a copper layer 40, a free ferromagneticlayer (NiFeCo) 35, a copper layer 40, and a composite ferromagnetic film(pinned layer) 50, which are laminated sequentially. The compositeferromagnetic film (pinned layer) 50 consists of Co 51 (35 Å), Ru 52 (6Å), and Co 53 (20 Å), which are laminated sequentially. Duringlamination a magnetic field is applied in the direction of the arrow200. Owing to the applied magnetic field, the composite ferromagneticfilm 50 has its axis of easy magnetization oriented in the directionperpendicular to the paper surface. The Co film 51 and the Co film 53are strongly coupled with each other in an antiferromagnetic manner, sothat they form a pinned layer of self-pinned type. Subsequently, anorganic resist film is laminated, and then it is patterned as desired. Afilm of permanent magnet (CoCrPt film) 80 is laminated. It is fabricatedin a desired shape. A layer of Nb/Au/Nb is laminated, and then it isfabricated to form an electrode 90. An insulating film (Al₂O₃ film) 100for magnetic gap is formed. An upper shield film (NiFe film) 110 islaminated and then it is fabricated in a desired shape. Thus there isobtained a magnetic head. The electrode spacing Tw is 0.5 μm and thesensor height hMR is 0.4 μm.

[0056] In this example, the pinned ferromagnetic layer 65 is magnetizedin the direction of the arrow 55. However, this direction may bereversed (180°). The composite ferromagnetic film 50 produces aneffective coercive force and hence forms the pinned layer of self-pinnedtype.

[0057] It was found that the giant magnetoresistive sensor in thisexample produces 1.5 times as large read-back output as the conventionalone and has good electro-static durability and good Asym.

[0058] Further, this example also demonstrates another giantmagnetoresistive sensor which is identical in structure with theabove-mentioned one, except that the thickness of the ferromagneticlayer is changed (Co 25 Å, Ru 6 Å, Co 20 Å) so that the effectivemagnetic moment of the composite ferromagnetic film 50 is almost null.The giant magnetoresistive sensor produces a large read-back output andhas good electro-static durability and good Asym.

EXAMPLE 6

[0059] This example demonstrates another giant magnetoresistive sensorhaving an antiferromagnetic layer as in Example 4. It consists of asubstrate, a lower shield film (NiFe film) 5, an insulating film (Al₂O₃)10 for magnetic gap, and a magnetoresistive film 30. Themagnetoresistive film 30 consists of a composite ferromagnetic film(pinned layer) 50, a copper layer 40, a pinned ferromagnetic layer(CoFe) 65, and an antiferromagnetic layer (PtMn) 70, which are laminatedsequentially. The composite ferromagnetic film (pinned layer) 50consists of Co 51 (20 A), Ru 52 (6 A), and Co 53 (35 A), which arelaminated sequentially. The composite ferromagnetic film 50 has its axisof easy magnetization oriented in the direction perpendicular to thepaper surface. The Co film 51 and the Co film 53 are strongly coupledwith each other in an antiferromagnetic manner, so that they form apinned layer of self-pinned type. Subsequently, an organic resist filmis laminated, and then it is patterned as desired. A film of permanentmagnet (CoCrPt film) 80 is laminated. It is fabricated in a desiredshape. A layer of Nb/Au/Nb is laminated, and then it is fabricated toform an electrode. An insulating film (Al₂O₃ film) for magnetic gap isformed. An upper shield film (NiFe film) is laminated and then it isfabricated in a desired shape. Thus there is obtained a magnetic head.

[0060] The giant magnetoresistive sensor in this example produces 1.5times as large read-back output as the conventional one and has goodelectro-static durability and good Asym.

EXAMPLE 7

[0061] This example demonstrates a thin-film magnetic head (ofread/write separate type) in which the magnetoresistance element of thepresent invention is used as the reading head and the conventionalinductive thin-film head is used as the writing head. FIG. 5 is a partlycut away perspective view showing this thin-film magnetic head. There isshown a substrate 5 (as a slider) which is a sintered body composedmainly of Al₂O₃.TiC. On the substrate are formed a lower shield film 10and an insulating film (Al₂O₃ film) for magnetic gap. On them is furtherformed a magnetoresistive film 30, which consists of a first freeferromagnetic film (NiFeCo), a copper layer, a composite ferromagneticfilm (pinned layer of self-pinned type), a copper layer, and a secondfree ferromagnetic film (NiFeCo), which are laminated sequentially. Theferromagnetic composite film (pinned layer of self-pinned type) iscomposed of Co (20 Å), Ru (6 Å), Co (35 Å), Ru (6 Å), and Co (20 Å),which are laminated sequentially. Subsequently, an organic resist filmis laminated, and then it is patterned as desired. A film of permanentmagnet (CoCrPt film) is laminated. It is fabricated in a desired shape.A layer of Nb/Au/Nb is laminated, and then it is fabricated to form anelectrode. An insulating film (Al₂O₃ film) for magnetic gap is formed. Amagnetic shield film (NiFe film) 110 is formed. The part produced asmentioned above functions as the reading head.

[0062] An inductive thin-film head is formed as the magnetic writinghead, which consists of an upper magnetic pole 120 and a coil 130. Theupper magnetic pole 120 is a 3.0-μm thick film of Ni-20 at % Fe alloywhich is formed by sputtering. The gap between the upper shield film 110and the upper magnetic pole 120 is filled with a 0.2-μm thick Al₂O₃ filmformed by sputtering. The coil 130 is a 3.0-μm thick copper film. Thelower magnetic pole 110 and the upper magnetic pole 120 are magneticallyconnected with each other to form a magnetic circuit. The coil 130intersects the magnetic circuit.

[0063] It was found that the thin-film magnetic head of this exampleproduces 1.5 times as large read-back output as the conventional one andhas good peak symmetry of read-back waveform, with Asym. depending onhMR very little.

EXAMPLE 8

[0064] This example demonstrates a magnetic disk apparatus equipped withthe magnetic head produced in the aforesaid examples of the presentinvention. It is schematically shown in FIG. 6.

[0065] There is shown a magnetic recording medium 140, which is made ofa Co—Ni—Pt—Ta alloy having a residual magnetic flux density of 0.45 T.The magnetic recording medium 140 is driven by a drive unit 150. Themagnetic head 160 is driven by the drive unit 170 so that it selects anytrack on the magnetic recording medium 140. Signals for the magnetichead 160 are processed by the read/write signal processing system 180.

[0066] The magnetoresistive sensor built into the magnetic head 160produces a larger reproduction output and better peak symmetry ofread-back waveform than the magnetoresistive sensor of conventionalstructure. Therefore, the magnetic disk apparatus equipped with it has anarrow track width and a high recording density.

[0067] As mentioned above, the present invention provides a giantmagnetoresistive sensor which produces a large reproduction output, goodpeak symmetry of read-back waveform, and good electro-static durability.

What is claimed is:
 1. A giant magnetoresistive sensor having amagnetoresistive film, a pair of electrodes to supply electric currentto said magnetoresistive film, and magnetic shield films formed on theupper and lower sides of said magnetoresistive film, characterized inthat said magnetoresistive film is composed of a first freeferromagnetic film, a first non-magnetic film, a composite ferromagneticfilm, a second non-magnetic film, and a second free ferromagnetic film,which are laminated sequentially, and said composite ferromagnetic filmcontains a first, second, and third ferromagnetic films, which areantiferromagnetically coupled with one another, and also contains filmswhich separate said ferromagnetic films from one another andantiferromagnetically couple them with one another.
 2. A giantmagnetoresistive sensor as defined in claim 1 , wherein the net magneticmoment of said composite ferromagnetic film is smaller than the magneticmoments in total of the first, second, and third ferromagnetic filmsconstituting said composite ferromagnetic film.
 3. A giantmagnetoresistive sensor as defined in claim 1 , wherein the total amountof magnetic moment of the first and third ferromagnetic films of saidcomposite ferromagnetic film is approximately equal to the magneticmoment of the second ferromagnetic film.
 4. A giant magnetoresistivesensor having a magnetoresistive film, a pair of electrodes to supplyelectric current to said magnetoresistive film, and magnetic shieldfilms formed on the upper and lower sides of said magnetoresistive film,characterized in that said magnetoresistive film is composed of a firstcomposite ferromagnetic film, a first non-magnetic film, a freeferromagnetic film, and a second composite ferromagnetic film, which arelaminated sequentially, and said first composite ferromagnetic film andsaid second composite ferromagnetic film contain a first and secondferromagnetic films, which are antiferromagnetically coupled with eachother, and also contain films which separate said ferromagnetic filmsfrom each other and antiferromagnetically couple them with each other.5. A giant magnetoresistive sensor as defined in claim 4 , wherein thenet magnetic moment of said first composite ferromagnetic film issmaller than the magnetic moments in total of the first and secondmagnetic films constituting said first composite ferromagnetic film andthe net magnetic moment of said second composite ferromagnetic film issmaller than the magnetic moments in total of the first and secondmagnetic films constituting said second composite ferromagnetic film. 6.A giant magnetoresistive sensor as defined in claim 4 , wherein themagnetic moments of the first and second ferromagnetic films of saidfirst or second composite ferromagnetic films are approximately equal toeach other.
 6. A thin-film read/write head which comprises an inductivethin-film head for magnetic recording and a giant magnetoresistivesensor as defined in any of claims 1 to 6 , said inductive thin-filmhead having a pair of magnetic poles, a magnetic circuit to magneticallycouple said pair of magnetic poles, and a coil intersecting saidmagnetic circuit.
 8. A magnetic recording apparatus which comprises amagnetic recording medium, a thin-film magnetic head mentioned in claim7 , a drive means to drive said magnetic recording medium and said headrelatively to each other, and a read/write signal processor connected tosaid head.